"One does not respond to criticism by cutting off heads," Rouhani said as he welcomed visiting Danish Foreign Minister Kristian Jensen to Tehran.

"I hope that European countries who always react on human rights matters will meet their duties."

Human rights groups frequently criticise use of the death penalty in Iran, where hanging is employed.

Rouhani also accused the Middle East's top Sunni Arab power of using the row over Nimr, which led a mob to ransack and set fire to the kingdom's embassy in Tehran, as an excuse to sever ties.

Saudi Arabia's consulate in second city Mashhad was also torched.

"Saudi Arabia cannot cover its crime of having cut off the head of a cleric by cutting relations," he said.

The violence was condemned by Rouhani, and Iran's judiciary has said 50 people involved in the incidents, including ringleaders, have been arrested and will face legal action.

Iran's mission at the United Nations also expressed "regret" at the fireraising and disobedience in a letter to the UN Security Council.

' Trade ties limited '

Before Rouhani spoke, a government spokesman, Mohammad Bagher Nobakht, said cutting diplomatic relations would not hurt Iran or damage its development.

Bahrain and Sudan also broke ties with Iran, and a number of other Arab countries have recalled their envoys, in sympathy with Riyadh.

Commerce between Iran and the countries that have severed relations is low, according to official figures released Tuesday by economic daily Donaye Eghtesad.

Bilateral trade between Iran and Saudi Arabia reached $172.5 million (159.7 million euros) during the first eight months of the Iranian year that began on March 20, 2015.

It comprised $132.2 million of Iranian exports, particularly fruit and steel, and $40.2 million of imports from Saudi Arabia, mainly fabrics and packaging products.

In the same period Iran exported $63.6 million of goods to Bahrain while buying only $60,000 worth from the Gulf state.

The tension with Saudi Arabia "will have no impact on Iran's national development," Nobakht said.

Instead, "it is Saudi Arabia that will suffer", he argued, reiterating Tehran's harsh criticism of Nimr's killing but condemning the violence by protesters as unjustified actions "beneath the dignity of the Iranian people".

And he compared Riyadh's "immature reaction" to the attacks with Iran's "restraint" after 464 Iranian pilgrims died in a stampede at the hajj in Saudi Arabia in September.

Nobahkt also said: "We condemn the inhumane, barbaric and Daesh-like execution of the cleric Sheikh Nimr," using the Arabic acronym for the Islamic State group.

He said Riyadh is trying to compensate for its political failures in regional conflicts, naming Iraq, Syria and Yemen.

Saudi Arabia and Shiite Iran have long competed for influence in the region.

Even before Nimr's execution, relations were strained over the two nations' backing opposing factions in Syria and Yemen.